This invention relates to transducers in general and more particularly to a capacitive transducer formed by integrated circuit technology.
The prior art includes a variety of devices which generally fall into the category of transducers. Many of these devices employ piezoresistive elements. Essentially, such elements exhibit a change in resistance as a function of applied pressure or force.
Piezoresistive devices may be mounted on a diaphragm which diaphragm deflects upon application of a force. The diaphragm can be fabricated from silicon or another semiconductor material. Hence the elements can be diffused into the diaphragm by conventional integrated circuit techniques.
Another class of pressure transducers employs a variation of capacitance to determine the magnitude of applied force. Essentially, these devices operate to vary the effect of capacitance between a movable plate and a stationary plate. The movable plate can also be a flexible diaphragm which will deflect upon application of a suitable force in an amount proportional to the force. Movement of the plate serves to vary the effective distance between this plate and the fixed plate. The operation of such devices is extremely well-known.
In any event, both types of transducers have their particular utility and associated advantages and disadvantages. Capacitive type transducers are usually difficult to fabricate and are not necessarily compatible with conventional integrated circuit techniques. The prior art has continuously attempted to fabricate a capacitive transducer utilizing integrated circuit techniques, but such devices are attendant with various problems.
For an example of a capacitive transducer employing integrated circuit techniques, reference is made to U.S. Pat. No. 3,748,541 entitled PRESSURE SENSITIVE TRANSDUCERS EMPLOYING CAPACITIVE AND RESISTIVE VARIATIONS issued on July 4, 1973 to A. D. Kurtz and assigned to Kulite Semiconductor Products, Inc., the assignee herein. As is evident from that patent and other patents which exist, there is also a desire to produce a capacitive transducer which can be hermetically sealed. This enables improved temperature operation and a more reliable and consistent circuit operation.
It is therefore an object of this invention to provide a capacitive transducer which is simple to fabricate and easy to use and which device can be mass produced.
A further object of this invention is to provide a capacitive transducer or a capacitor which may be variable or of a fixed value depending upon the particular application.
Another object of this invention is to provide a capacitive transducer which can be hermetically sealed and which can provide controllable values of capacitance.
A further object of this invention is to provide a means of avoiding stray capacitance of PN junction by dielectrically isolating the two capacitor plates from the resulting mechanical structure.